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Current time:0:00Total duration:6:38

Video transcript

in a previous video we gave an overview of the light dependent reactions what are essentially occurring across the silo or within or across the thylakoid membrane right and that we zoomed in on one and we saw okay we have some energy from light exciting the electrons within the that chlorophyll pair that p680 chlorophyll a pair that electron that energized electron will then be transferred from one molecule to another and as it does so it'll go to lower and lower energy states and that released energy some of it will be used to transfer hydrogen protons across the membrane and then eventually that electron will make its way to photosystem 1 where it can get excited again if we think of it as the same electron it doesn't necessarily have to be the exact same electron but we can we can think of that same electron as being excited again by light energy and then it can once again go to lower and lower energy states and this time it's going to be used to reduce nadp+ to nadph now NADPH itself is an input into the Calvin cycle but ATP is another input we need for the Calvin cycle and the way that we produce ATP is that hydrogen ion concentration that increases on the inside due to it being essentially pumped across the membrane as well as the leftover hydrogen ions from the water after it's stripped of electrons to replace that excited that originally excited electron and pee in that p680 chlorophyll pair well that increased hydrogen ion concentration can be used to drive ATP synthase which creates ATP from phosphate and ADP and we saw it we saw that over here without seeing the different components you get light excite the electron the electron goes to lower and lower energy states as it does so as it's going from photosystem 2 to photosystem 1 some of that Energy's being used to pump hydrogen ions into the into the thylakoid lumen then that electron gets excited getting excited again and then as it gets transferred and goes to lower and lower energy states it can be used to produce nadph where once again its electrons are still at a fairly high I energy state so it's a strong reducing agent and so that's why it's valuable in the Calvin cycle that energy from acting as a strong reducing agent can be used to or helped in the creation or the eventual creation of the sugar and once again where is that electron once it gives it away how does it get replaced well it snags it from the water what I have here is a more detailed diagram that labels some of the actors and the important thing is really what we just covered and what we covered in more detail in the previous video the conceptual idea of what's happening in the light dependent reactions but a lot of times in your biology class or in your biology book you'll see the talk of things like a cytochrome complex and plasto quinone and and things like that and I want you to I want to look at that right now so that you're not intimidated when you see it and that you see that these are just the actors that we talked about so right over here this is photosystem two and and what you have and I give credit for where this image comes from it's modified from the light dependent reactions of photosynthesis figure eight by openstax college but this right over here we see the light is the light is interacting the way it's depicted here not directly with the chlorophyll pair within photosystem two that P that p680 chlorophyll chlorophyll a pair we see it acting on some of these neighboring molecules as their electrons get excited and then go to lower energy levels that energy can use to can be used to excite neighboring electrons this kind of keeps happening that energy gets transferred eventually to excite the electron in that p60 a pair and then that electron it's the first electron acceptor you'll see this sometimes is spoken of in your biology textbooks is pheophytin and then it that can then transfer the electron to plastoquinone and that plastic we known is inter interacting in this cytochrome complex which transfers the electron from plastoquinone to plasto sign in and as it's doing it you see the hydrogen ions being transferred from the outside of the thylakoid to the inside of the thylakoid which is exactly what we've been talking about and then as we go to photosystem one well that electron can be transferred from the plastocyanin to the chlorophyll pair the p700 chlorophyll that can get excited again once again it doesn't have to be the light directly exciting it it can be exciting other molecules within the within the photosystem with in photosystem one but that energy eventually gets transferred to though to that chlorophyll excites its electrons and then it goes from it goes from one molecule to another eventually gets goes to ferredoxin which is being used in conjunction it's one of the actors along it that the enzyme nadp+ reductase needs along with nadp+ so it's essentially just reducing nadp+ along with this electron that's on the ferredoxin to produce nadph and once again what's going on here well this is the ATP synthase that is using all this increased hydrogen ion concentration on the inside of the thylakoid to pump or too few to power the you could say the motor or that the ATP synthase is the motor that is powered as these hydrogen ions go down their concentration gradient and that energy is used to jam the phosphate onto the ADP to produce ATP so I've said essentially the same thing two or three times already in the last two or three videos but I'm just doing it because when you first see this it seems very very intimidating and very very complex and it is complex and frankly it's amazing that things like this are happening on the plant that I'm looking at outside of my window right now and it kind of boggles my mind that this kind of thing is happening in nature and there are you know bits and pieces of it that aren't fully understood yet and still need to be discovered but at the same time the general idea is that as intimidating as these diagrams appear so hopefully you find this all inspiring like I do and not as intimidating as what some of these words might make you feel initially
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